Dual-acting shock absorbers utilized on vehicles usually consists of a hollow cylinder defining an internal chamber which is divided into a compression compartment and an expansion compartment by a piston slidably positioned in the internal chamber. The piston includes internal valving which permits fluid to flow between the compression and rebound compartments as the piston moves within the internal chamber.
A closed end of the cylinder is connected to the unsprung mass of the vehicle by a suitable linkage. A piston rod extends through a seal assembly mounted in the other end of the cylinder for movement relative to the cylinder. The piston rod has its inner end connected to the piston for movement therewith and its projecting and terminates in a linkage connectable to the sprung mass of the vehicle.
The damping characteristics of such shock absorbers are determined by the rate at which fluid is permitted to flow between the rebound and compression compartments. This rate, in turn, controls the speed at which the piston may move in the cylinder responsive to the external forces applied to the shock absorber.
Those working in the art have long recognized the desirability of being able to change or adjust the rate of fluid flow so that the damping characteristics of a shock absorber of this type may be changed to accommodate different, anticipated conditions. Adjustable damping shock absorbers have been proposed in the past and have included mechanisms for selectively changing the rate of fluid flow. These prior mechanisms share the disadvantages of requiring structurally complex individual components. The complexity is a result of the need to provide adjustment of the primary fluid flow path of the shock absorber, the inaccessibility of the location of the flow adjustment, and the need to provide for adjustment over a wide range of flows. This complexity results in relatively high fabrication or assembly costs.
Additionally in many of these prior mechanisms, adjustment of the flow rate requires the collapsing of the shock absorber and rotation of the piston against a retaining mechanism. Others require careful adjustment and securing of the mechanism. This need to so manipulate the shock absorber to adjust the damping characteristics has made these prior shock absorbers not only expensive but difficult to commercialize.